This invention relates to tilt tray sortation conveyors and more particularly to improvements in such conveyors.
Tilt tray sortation conveyors have been in use for some time. Such sorters utilize a track, formed into a closed loop to support and guide a series of chain connected carriages. A tiltable tray is mounted on each carriage for tipping to either side at a sort location by remotely controlled tip-up apparatus mounted on either side of the track.
Objects to be sorted are loaded onto the trays either manually or automatically at an induction station. The loaded trays are conveyed along the track until they reach the appropriate sort location discharge chute disposed beside the track. The tray is then tipped at the appropriate time to discharge the package into the desired discharge chute.
In one prior system, each tray is mounted to a cast aluminum support which is pivoted on a four wheel carriage. The carriages are bolted to a roller chain which maintains their separation and pulls them along the track via an hydraulically driven drive sprocket. The supports are latched to the carriages to hold the support and tray in a level or horizontal position. A spring-loaded lever arm pivoted to the support has a ramp on each side for engaging a selectively activated tip-up roller to facilitate unlatching of the support from the carriage and then tipping of the tray.
When it is desired to tip the tray, an air cylinder lifts a roller tipped arm into the path of the ramp. Upon making contact with the roller, a first cam section of the ramp raises the lever arm against its spring bias and releases the latch. Continuing engagement of the roller with the remaining cam section of the ramp tips the tray to the desired side.
Two configurations of this type sorter are currently in production by applicant. They differ primarily in the weight capacity of the objects they can sort. One, for example, is intended for objects weighing up to 200 lb, while the other is intended for objects weighing up to 50 lb.
Details of such systems and variations thereof are also shown in several prior patents belonging to applicant. A general system is described in U.S. Pat. No. 3,034,665. One type of unlatch and tipping ramp is described in U.S. Pat. No. 3,510,014, and another in U.S. Pat. No. 3,630,394. A tip-up and mounting apparatus is disclosed in U.S. Pat. No. 4,174,773 and a modified yieldable latch is disclosed in U.S. Pat. No. 4,089,404. These patents are incorporated herein by reference for further background information.
While the tilt tray sortation conveyors now produced by applicant have found many applications and uses, current sortation environments require high sortation throughput which is beginning to exceed the design parameters of the current systems. Applications tend to be heading toward handling smaller packages and higher speeds, while current systems tend to work best in low speed, heavy duty applications. Increasing sortation throughput requirements demand conveyor or carriage speeds which have gradually increased to double the original most efficient design speeds of the present systems.
When considering the desirability of increased sortation throughput, it is not generally suitable to merely increase the speeds of the current carriage and tray structures, due in part to the relationship of the speed of the carriage and the shape of the cam or ramps on the lever arm. This relationship plays a very important role in determining the characteristics of the tray tipping and article discharge action. When the carriage speed and the ramp shapes are correctly matched, the objects on the tray are smoothly unloaded. When the two are not matched, however, many problems result.
For example, the acceleration of the tray in a tipping direction, which is perpendicular to the carriage movement, is a function of both carriage speed and cam or ramp shape. As carriage speeds are increased, tray tipping accelerations are increased. Packages on the rising side of the trays can be catapulted off, missing the target discharge chute. Where the tray acceleration exceeds that of a falling body, packages on the descending tray side are left with no support and also "fly". Since the packages may be highly varied in shape and weight, the flight characteristics are highly varied, random, and cannot be accurately anticipated for a particular sort or discharge operation.
Of course, one way to accommodate increased carriage speeds and increasing tilt tray acceleration is to simply widen the target mouth of the discharge chute, to a condition where all packages will be received regardless of their "flight" parameters. This tends, however, to detract from overall sorter throughput since it decreases the number of sort stations or discharge chutes for a given conveyor length. Even though the carriages run faster, there are less sort stations and fewer sort possibilities. It is thus difficult to increase sortation throughput merely by increasing carriage speed.
There are additional problems associated with increasing the carriage speeds of tilt tray sorters of present construction. For example, when tray speeds are increased, the consequential increasing tray acceleration can cause packages or articles to tumble. While certain article shapes are more prone to tumbling than others, any tumbling is undesirable for several reasons. First, tumbling of fragile packages may cause breakage or damage to products therein. Secondly, tumbling may interfere with sortation or conveying controls. In some instances a readable code is applied to a selected surface of a package. Scanners read the code on a discharging package for confirmation or downstream control. A tumbled package may not present the code in proper position for scanning. Thirdly, tumbling upsets the orientation of the package. A particular package orientation may be desired for palletizing, further conveying or the like.
In addition, operation at higher speeds results in excessive mechanical wear from impacts between components. At higher speeds the lever arm actuated index plate bounces off the latching pin causing improper interaction between the tip up roller and the index arm. Loads are catapulted, or the rebounding trays relatch in horizontal position and trap light packages, carrying them beyond the sort location. Overall noise levels are excessive.
There have been several attempts at providing improved ramps on the lever arms. U.S. Pat. No. 3,510,014 provides a ramp having a steep incline for unlatching and a lesser incline for tilting. U.S. Pat. No. 3,630,394 attempts to define a ramp shape either in the form of a parabola, which is in part a function of carriage speed, or in the form of an arc of a specific circle. Nevertheless, present day increased sortation throughput requires greater tray acceleration control and a greater reduction in forces exerted on the components of the entire system than can be provided by these prior structures. The lever arm ramps of these disclosures are attended with the problems noted when operated at currently desired speeds.